1. Field of the Invention
The present invention generally relates to an electroluminescent (to be abbreviated as xe2x80x9cELxe2x80x9d hereinafter) device with a drying film and a method for fabricating the same. The EL device is characterized in that an alkaline-earth metal film composed of barium (Ba), magnesium (Mg) or calcium (Ca) is employed to react with oxygen and form, during the evaporation process for forming the alkaline-earth metal film, an oxide film composed of barium oxide (BaO), magnesium oxide (MgO) or calcium oxide (CaO) functioning as a drying film on the surface of an opposed electrode, so as to prevent the generation of dark spots and to improve the reliability of the device.
2. Description of the Prior Art
The organic EL device has attracted tremendous attention due to its advantages over other display panels. These advantages include larger visual angle, shorter response time, smaller dimension in thickness, lower power consumption, simpler fabrication, no need for backlighting, and the ability for light emitting in a full color range.
Please refer to FIG. 1, which a cross-sectional view showing the structure of an organic EL device in accordance with the prior art. The organic EL device is characterized in that a transparent electrode 12 is formed on a substrate 11, and on the transparent electrode 12 there are an organic layer 13 comprising a hole injection layer, a hole transport layer, an organic emitting layer or an electron transport layer, an opposed electrode 14 and an sealing case 15 are formed by evaporation in turn. Since in an organic EL device the light is generated when the electrons and holes from the transparent electrode 12 and opposed electrode 14 combine in the organic layer 13 to excite the organic emitting layer, it is inevitable that heat is generated during the luminescence process. Once the heat encounters the moisture existing inside the sealing case 15, dark spots due to oxidation will be formed on the surface of the organic layer 13. The existence of such dark spots adversely affects the luminescence qualities such as luminescence intensity and luminescence uniformity of an organic EL device. More seriously, the lifetime of an organic EL device may be substantially shortened.
In order to overcome the image defects due to the undesirable dark spots, some companies have developed a number of prior art organic EL displays to improve the image quality. For example, in the Japanese Patent Nos. JP-A-363890 and JP-A-5-114486, it is disclosed that liquid fluorinated carbon is disposed inside the sealing case 15 to effectively remove the heat generated during the luminescence process. In the Japanese Patent No. JP-A-5-41281, it is disclosed that dehydrating agents such as a synthetic zeolite are mixed in the liquid fluorinated carbon to effectively remove the moisture existing in the periphery of the device.
The above prior arts can reduce the generation of dark spots to some extent; however, the dehydrating agents such as liquid fluorinated carbon may add difficulty to the fabrication process, which is unfavorable for fabrication integration and reduction in cost.
Accordingly, a second prior art structure of an organic EL device is proposed as shown in FIG. 2. In the U.S. Pat. No. 5,882,761, entitled xe2x80x9cOrganic EL elementxe2x80x9d, it is disclosed that a drying film 17 is attached to the inner surface of a sealing case 15 and an internal space 19 is formed between the drying film 17 and an opposed electrode 14. The solid-state drying film 17 absorbs the moisture existing inside the sealing case 15, so as to prevent the generation of dark spots.
Even though the U.S. Pat. No. 5,882,761 can overcome some of the problems in the prior arts, it still has the following drawbacks:
1. The drying film is attached in the direction perpendicular to the organic layer and the opposed electrode. Therefore, when the device is hit against an external force, the drying film may fall off and directly hit the organic layer or the opposed electrode. In this case, the device will be damaged.
2. The conventionally used temperature for forming such a drying film is higher than 2000xc2x0 C. This high-temperature condition may adversely affect the fabrication yield and the operation reliability of the organic layer.
3. The drying film is attached in the direction perpendicular to the organic layer and the opposed electrode. In addition, there must be a vertical gap between the drying film and the opposed electrode. Therefore, the total height is increased, which becomes a limit when it comes to designing a downsized device.
Therefore, the present invention has been made to solve such problems in view of the forgoing status and to further provide an electroluminescent (EL) device, incorporating a drying film directly formed on the surface of the opposed electrode. In this case, the fabrication yield and the operation reliability of the organic layer will not be affected and the generation of dark spots can be prevented, therefore the lifetime of the device is prolonged.
It is the primary object of the present invention to provide a method for fabricating an EL device with a drying film, characterized in that an alkaline-earth metal film composed of barium (Ba), magnesium (Mg) or calcium (Ca) is employed to react with oxygen and form, during the evaporation process for forming the alkaline-earth metal film, an oxide composed of barium oxide (BaO), magnesium oxide (MgO) or calcium oxide (CaO) functioning as a drying film on the surface of an opposed electrode such that the temperature for forming the drying film is substantially reduced. In this case, the operation reliability of the organic layer will not be affected and the generation of dark spots can be prevented so that the lifetime of the device can be prolonged.
It is another object of the present invention to provide an EL device with a drying film, wherein the drying film is formed directly on an opposed electrode at a relatively lowered fabrication temperature. In this case, the drying film may not fall off and damage the device. Moreover, a dry environment is maintained inside the EL device so as to prevent the generation of dark spots and prolong the lifetime of the device.
It is still another object of the present invention to provide an EL device with a drying film, wherein the drying film is directly formed on an opposed electrode, so that the fabrication process can be simplified and the size of the device can be minimized. In this case, the fabrication cost is substantially lowered.
In order to achieve the foregoing objects, the present invention provides a method for fabricating an EL device with a drying film, comprising the steps of: providing a substrate; forming, in sequence from substrate up, a transparent electrode, a luminescent layer, and an opposed electrode; and forming a drying film by providing a raw material to react with a gaseous reactant on the surface of said opposed electrode.
The present invention further provides an EL device with a drying film, comprising: a substrate; at least one transparent electrode formed on the surface of said substrate; an organic layer formed on the surface of said transparent electrode; an opposed electrode formed on the surface of said organic layer; and a drying film formed on the surface of said opposed electrode, wherein said drying film is formed by providing a raw material to react with a gaseous reactant on the surface of said opposed electrode.
Other and further features, advantages and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings are incorporated in and constitute a part of this application and, together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like parts throughout the disclosure.